Re: Subquery with IN or EXISTS

Hi A.,

On 26 Sep 2001 07:24:41 -0700, anssiman(at)my-deja(dot)com (A. Mannisto)
wrote:

>Hello,
>
>does anybody know why this:
>SELECT * FROM tab WHERE col1 IN (SELECT col2 FROM TAB2)
>
>equals this:
>SELECT * FROM tab WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 =
>col2)
>
>but this:
>SELECT * FROM tab WHERE col1 IN (SELECT col2 FROM TAB2 WHERE
>col3='huu')
>
>equals _NOT_ this:
>SELECT * FROM tab WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 =
>col2 AND col3='huu')
>
>E.g. resultset is not the same in last two statements.
>Can I get same set as IN statement somehow using EXISTS (performance
>issue)?

I cannot reproduce your problem, results are equal here with
PostgreSQL 7.1.3. Could you post your CREATE TABLE and INSERT
statements?

Re performance: There's more than one way to do it. (Where did I hear
this before? ;-)) You might try:

SELECT tab.* FROM tab, tab2 WHERE tab.col1 = tab2.col2;

or SELECT DISTINCT ... , if col2 is not unique in tab2.

Kind regards,
Carl van Tast